1. Field of the Invention
Embodiments of the present invention generally relate to nuclear medicine, and systems for obtaining images of a patient's body organs of interest. In particular, the present invention relates to novel methods, apparatuses, computer readable mediums, and systems for reducing the number of radiation detectors used to cover a given axial field of view.
2. Description of the Related Art
Nuclear medicine is a unique medical specialty wherein radiation is used to produce images that show the function and anatomy of organs, bones and/or tissues of the body. Radiopharmaceuticals are introduced into the body, either by injection, inhalation, or ingestion, and are attracted to specific organs, bones and/or tissues of interest. For example, the radiopharmaceutical (e.g., rubidium) is injected into the bloodstream to image cardiac blood flow.
The radiopharmaceutical produces gamma photon emissions that emanate from the body. One or more detectors are used to detect the emitted gamma photons and the information collected from the detector(s) is processed to calculate the position of origin of the emitted photon from the source (i.e., the body organ or tissue under study). The accumulation of a large number of events (e.g., a single gamma when using Single Photon Emission Computed Tomography (“SPECT”) and coincident gamma events when using Positron Emission Tomography (“PET”)) allows an image of the organ or tissue under study to be displayed.
FIG. 1 shows a system 100 which includes a known apparatus 102 for superposed MR and PET imaging. The apparatus 102 includes a known MR tube 104. The MR tube 104 defines a longitudinal direction Z (not shown), parallel to a longitudinal axis of a patient (also not shown), which extends orthogonally with respect to the plane of the drawing in FIG. 1.
As shown in FIG. 1, a plurality of PET detector units 106 arranged in pairs opposite each other about the longitudinal direction z are arranged coaxially within the PET scanner 104. The PET detector units 106 preferably include an Avalanche photodiode (“APD”) array 108 with an upstream array of Lutetium Oxyorthosilicate (“LSO”) crystals 110 and an electrical amplifier circuit (“AMP”) 112.
A computer 120 is also included in the system 100. The computer 120 includes a central processing unit (“CPU”) 114 for image processing of superposed MR and PET imaging, a user interface 118 (depicted as a keyboard), and a monitor 116 for viewing input and output data.
A PET scanner utilizes a large number of detectors (typically organized in blocks of scintillators) arranged around the patient in rings or in panels covering the largest possible solid angle. Scintillator material and associated photo-detectors and electronic channels are expensive.
In order to reduce cost, two approaches have been used, but both come with shortcomings: one approach is to shorten the length of the scintillator (e.g., to shorten the length from 2 cm to about 1.5 cm) and the second approach is to use a partial ring rotating tomograph (e.g., as described in David W. Townsend et al., A Rotating PET Scanner Using BOO Block Detectors: Design, Performance and Applications, 34 J Nucl Med 1367-1376 (1993)). Shortening the length of the crystal reduces the efficiency of the crystal (e.g., shortening the length of the crystal by 20% also reduces the efficiency of the crystal by 20%) and requires building new block detectors (which is relatively expensive).
Thus there is a need in the art for a lower cost scanner with substantially the same axial field-of-view (“FOV”) (with little or no detector or gantry motion), re-configuration of existing PET/CT scanners into a lower cost scanner with substantially the same axial FOV (with little or no detector or gantry motion), and a PET scanner with transmission capability (with no requirement of computerized tomography (“CT”) or magnetic resonance (“MR”) for attenuation purposes).